Urban physics

Urban Physics is the multiscale and interdisciplinary research area dealing with physical processes in urban environments that influence our everyday health, comfort and productivity. It involves disciplines ranging from mesoscale meteorology to human thermophysiology. The introductory lecture addresses basic research on numerical modeling of microscale atmospheric boundary layer processes as well as practical applications such as outdoor air pollution, pedestrian wind comfort and the urban heat island effect

Urban physics

Urban Physics is the multiscale and interdisciplinary research area dealing with physical processes in urban environments that influence our everyday health, comfort and productivity. It involves disciplines ranging from mesoscale meteorology to human thermophysiology. The introductory lecture addresses basic research on numerical modeling of microscale atmospheric boundary layer processes as well as practical applications such as outdoor air pollution, pedestrian wind comfort and the urban heat island effect

Impact, runoff and drying of wind-driven rain on a window glass surface: numerical modelling based on experimental validation

This paper presents a combination of two models to study both the impingement and the contact and surface phenomena of rainwater on a glass window surface: a Computational Fluid Dynamics (CFD) model for the calculation of the distribution of the wind-driven rain (WDR) across the building facade and a semi-empirical droplet-behaviour model. The CFD model comprises the calculation of the wind-flow pattern, the raindrop trajectories and the specific catch ratio as a measure of the WDR falling onto different parts of the facade. The droplet-behaviour model uses the output of the CFD model to simulate the behaviour of individual raindrops on the window glass surface, including runoff, coalescence and drying. The models are applied for a small window glass surface of a two-storey building. It is shown that by far not all WDR that impinges on a glass surface runs off, due to evaporation of drops adhered to the surface. The reduction of runoff by evaporation is 26% for a typical cumuliform rain event and 4% for a typical stratiform rain event. These models can be used to provide the knowledge about WDR impact, runoff and evaporation that is needed for the performance assessment of selfcleaning glass or the study of the leaching of nanoparticles from building facades

Computational Fluid Dynamics simulations of wind-driven rain on a low-rise building : new validation efforts

Despite the establishment of CFD as a tool for calculating the amount of wind-driven rain (WDR) falling onto building facades, very few efforts have been made towards the validation of CFD for this purpose. This paper presents part of a detailed CFD validation study that was conducted at the Laboratory of Building Physics, supported by a new experimental wind, rain and WDR database for a low-rise building. It will be shown that numerical simulation, if conducted with care, can provide quite accurate predictions of the amount of WDR impinging on the building facade and that the main discrepancies in this case were due to a simplification of the upstream wind conditions in the numerical model

Air pollutant dispersion from a large semi-enclosed stadium in an urban area: high-resolution CFD modeling versus full-scale measurements

Abstract: High-resolution CFD simulations and full-scale measurements have been performed to assess the dispersion of air pollutants (CO2) from the large semi-enclosed Amsterdam ArenA football stadium. The dispersion process is driven by natural ventilation by the urban wind flow and by buoyancy, and by the interaction between outdoor wind flow and indoor airflow which are only connected by the relatively small ventilation openings in the stadium facade. The CFD simulations are performed with the 3D Reynolds-averaged Navier-Stokes equations supplemented with the realizable k-e model to provide closure. The full-scale measurements include reference wind speed, wind direction, and outdoor and indoor air temperature, water vapor and indoor CO2 concentration. In particular, the focus is on CFD simulations and measurements for the few hours immediately after a concert, when the stadium roof remains closed and when indoor air temperature,water vapor and CO2 concentration have reached a maximum level due to the attendants. The removal of the sources/attendants allows an assessment of the natural ventilation rate using the concentration decay method. The CFD simulations compare favorably with the measurements in terms of mean wind velocity in the main ventilation openings and in terms of the CO2 concentration decay after the concerts. The validated CFD model will in the future be used for a detailed evaluation of indoor concentration gradients and the interaction between wind-induced and buoyancy-induced natural ventilation

Validation of external BES-CFD coupling by inter-model comparison

Conflation of computational fluid dynamics (CFD) and building energy simulation (BES) has been used in recent years in order to improve the estimation of surface coefficients for studies on thermal comfort, mold growth and other performance aspects of a building. BES can provide more realistic boundary conditions for CFD, while CFD can provide higher resolution modelling of flow patterns within air volumes and convective heat transfer coefficients (CHTC) for BES. BES and CFD can be internally or externally coupled. Internal coupling is the traditional way of expanding software by which the code is expanded by adding new modules and it entails a lot of effort in terms of debugging, maintenance etc. On the other hand, by external coupling different existing numerical packages work together, using the latest advances already implemented in them.This paper focuses on the validation of a newly developed prototype performing the external coupling of BES and CFD. The validation procedure involves an inter-model comparison between a conjugate heat transfer model and the prototype

Validation of external BES-CFD coupling by inter-model comparison

Conflation of computational fluid dynamics (CFD) and building energy simulation (BES) has been used in recent years in order to improve the estimation of surface coefficients for studies on thermal comfort, mold growth and other performance aspects of a building. BES can provide more realistic boundary conditions for CFD, while CFD can provide higher resolution modelling of flow patterns within air volumes and convective heat transfer coefficients (CHTC) for BES. BES and CFD can be internally or externally coupled. Internal coupling is the traditional way of expanding software by which the code is expanded by adding new modules and it entails a lot of effort in terms of debugging, maintenance etc. On the other hand, by external coupling different existing numerical packages work together, using the latest advances already implemented in them.This paper focuses on the validation of a newly developed prototype performing the external coupling of BES and CFD. The validation procedure involves an inter-model comparison between a conjugate heat transfer model and the prototype

Application of externally-coupled BES-CFD in HAM engineering of the indoor environment

The high importance of indoor environment performance aspects such as surface condensation, mold growth, thermal comfort, etc., is widely recognized. High-resolution simulation of heat, air and moisture (HAM) transfer can be used to enhance the prediction and analysis of these aspects. For this purpose, a coupling mechanism has been developed in order to perform run-time external coupling between Building Energy simulation (BES) and Computational Fluid Dynamics (CFD). This paper presents the results of indoor humidity calculation using the new coupled tool for the BESTEST case- 600. The results are compared with stand-alone BES results and the need and importance of coupled simulations is discussed

Uncertainties due to the use of surface averaged wind pressure coefficients

A common practice, adopted by several building energy simulation (BES) tools, is the use of surface averaged wind pressure coefficients (Cp) instead of local Cp values with high resolution in space. The aim of this paper is to assess the uncertainty related to the use of surface averaged data, for the case of a cubic building with two openings. The focus is on wind-driven ventilation and infiltration, while buoyancy is not taken into account. The study is performed using published empirical data on pressure coefficients obtained from wind tunnel tests. The method developed to calculate the uncertainty is based on comparison of: the flow rate calculated using the averaged values (fAV), and the one calculated using local values (fLOC). The study considers a large number of combinations for the opening positions in the facade. For each pair of openings (i), the values of fLOC_i and fAV_i are calculated. Based on the ratio between fLOC_i and fAV_i the relative error (ri) is calculated. The relative error is presented statistically, providing probability density graphs and upper and lower bounds for the confidence interval (CI) of 95%. For this CI, the conclusion is that 0.24 fAV <fLOC <4.87 fAV

External coupling between BES and HAM programs for whole building simulation

This paper discusses a procedure for the two-way runtime external coupling between Building EnergySimulation (BES) and building envelope Heat, Air and Moisture (HAM) programs for enhanced wholebuilding simulation. The coupling procedure presented here involves a description of the relevant physical phenomena at the interface between the programs, domain overlaps, coupling variables, coupling strategy and types of boundary condition. The procedure is applied using the programs ESP-r and HAMFEM, where the implementation and verification issues are discussed. This work concludes that the coupling between BES and HAM programs is feasible, and it can potentially enhance the accuracy in whole-building simulation